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/*
* Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License").
* You may not use this file except in compliance with the License.
* A copy of the License is located at
*
* http://aws.amazon.com/apache2.0
*
* or in the "license" file accompanying this file. This file is distributed
* on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
* express or implied. See the License for the specific language governing
* permissions and limitations under the License.
*/
#include "tls/s2n_tls13_handshake.h"
#include "tls/s2n_cipher_suites.h"
#include "tls/s2n_key_log.h"
#include "tls/s2n_security_policies.h"
static int s2n_zero_sequence_number(struct s2n_connection *conn, s2n_mode mode)
{
POSIX_ENSURE_REF(conn);
struct s2n_blob sequence_number;
if (mode == S2N_CLIENT) {
POSIX_GUARD(s2n_blob_init(&sequence_number, conn->secure.client_sequence_number, sizeof(conn->secure.client_sequence_number)));
} else {
POSIX_GUARD(s2n_blob_init(&sequence_number, conn->secure.server_sequence_number, sizeof(conn->secure.server_sequence_number)));
}
POSIX_GUARD(s2n_blob_zero(&sequence_number));
return S2N_SUCCESS;
}
int s2n_tls13_mac_verify(struct s2n_tls13_keys *keys, struct s2n_blob *finished_verify, struct s2n_blob *wire_verify)
{
POSIX_ENSURE_REF(wire_verify->data);
POSIX_ENSURE_EQ(wire_verify->size, keys->size);
S2N_ERROR_IF(!s2n_constant_time_equals(finished_verify->data, wire_verify->data, keys->size), S2N_ERR_BAD_MESSAGE);
return S2N_SUCCESS;
}
int s2n_tls13_keys_from_conn(struct s2n_tls13_keys *keys, struct s2n_connection *conn)
{
POSIX_GUARD(s2n_tls13_keys_init(keys, conn->secure.cipher_suite->prf_alg));
return S2N_SUCCESS;
}
int s2n_tls13_compute_ecc_shared_secret(struct s2n_connection *conn, struct s2n_blob *shared_secret) {
POSIX_ENSURE_REF(conn);
const struct s2n_ecc_preferences *ecc_preferences = NULL;
POSIX_GUARD(s2n_connection_get_ecc_preferences(conn, &ecc_preferences));
POSIX_ENSURE_REF(ecc_preferences);
struct s2n_ecc_evp_params *server_key = &conn->kex_params.server_ecc_evp_params;
POSIX_ENSURE_REF(server_key);
POSIX_ENSURE_REF(server_key->negotiated_curve);
struct s2n_ecc_evp_params *client_key = &conn->kex_params.client_ecc_evp_params;
POSIX_ENSURE_REF(client_key);
POSIX_ENSURE_REF(client_key->negotiated_curve);
POSIX_ENSURE_EQ(server_key->negotiated_curve, client_key->negotiated_curve);
if (conn->mode == S2N_CLIENT) {
POSIX_GUARD(s2n_ecc_evp_compute_shared_secret_from_params(client_key, server_key, shared_secret));
} else {
POSIX_GUARD(s2n_ecc_evp_compute_shared_secret_from_params(server_key, client_key, shared_secret));
}
return S2N_SUCCESS;
}
/* Computes the ECDHE+PQKEM hybrid shared secret as defined in
* https://tools.ietf.org/html/draft-stebila-tls-hybrid-design */
int s2n_tls13_compute_pq_hybrid_shared_secret(struct s2n_connection *conn, struct s2n_blob *shared_secret) {
POSIX_ENSURE_REF(conn);
POSIX_ENSURE_REF(shared_secret);
/* conn->kex_params.server_ecc_evp_params should be set only during a classic/non-hybrid handshake */
POSIX_ENSURE_EQ(NULL, conn->kex_params.server_ecc_evp_params.negotiated_curve);
POSIX_ENSURE_EQ(NULL, conn->kex_params.server_ecc_evp_params.evp_pkey);
struct s2n_kem_group_params *server_kem_group_params = &conn->kex_params.server_kem_group_params;
POSIX_ENSURE_REF(server_kem_group_params);
struct s2n_ecc_evp_params *server_ecc_params = &server_kem_group_params->ecc_params;
POSIX_ENSURE_REF(server_ecc_params);
struct s2n_kem_group_params *client_kem_group_params = &conn->kex_params.client_kem_group_params;
POSIX_ENSURE_REF(client_kem_group_params);
struct s2n_ecc_evp_params *client_ecc_params = &client_kem_group_params->ecc_params;
POSIX_ENSURE_REF(client_ecc_params);
DEFER_CLEANUP(struct s2n_blob ecdhe_shared_secret = { 0 }, s2n_blob_zeroize_free);
/* Compute the ECDHE shared secret, and retrieve the PQ shared secret. */
if (conn->mode == S2N_CLIENT) {
POSIX_GUARD(s2n_ecc_evp_compute_shared_secret_from_params(client_ecc_params, server_ecc_params, &ecdhe_shared_secret));
} else {
POSIX_GUARD(s2n_ecc_evp_compute_shared_secret_from_params(server_ecc_params, client_ecc_params, &ecdhe_shared_secret));
}
struct s2n_blob *pq_shared_secret = &client_kem_group_params->kem_params.shared_secret;
POSIX_ENSURE_REF(pq_shared_secret);
POSIX_ENSURE_REF(pq_shared_secret->data);
const struct s2n_kem_group *negotiated_kem_group = conn->kex_params.server_kem_group_params.kem_group;
POSIX_ENSURE_REF(negotiated_kem_group);
POSIX_ENSURE_REF(negotiated_kem_group->kem);
POSIX_ENSURE_EQ(pq_shared_secret->size, negotiated_kem_group->kem->shared_secret_key_length);
/* Construct the concatenated/hybrid shared secret */
uint32_t hybrid_shared_secret_size = ecdhe_shared_secret.size + negotiated_kem_group->kem->shared_secret_key_length;
POSIX_GUARD(s2n_alloc(shared_secret, hybrid_shared_secret_size));
struct s2n_stuffer stuffer_combiner = { 0 };
POSIX_GUARD(s2n_stuffer_init(&stuffer_combiner, shared_secret));
POSIX_GUARD(s2n_stuffer_write(&stuffer_combiner, &ecdhe_shared_secret));
POSIX_GUARD(s2n_stuffer_write(&stuffer_combiner, pq_shared_secret));
return S2N_SUCCESS;
}
static int s2n_tls13_pq_hybrid_supported(struct s2n_connection *conn) {
return conn->kex_params.server_kem_group_params.kem_group != NULL;
}
int s2n_tls13_compute_shared_secret(struct s2n_connection *conn, struct s2n_blob *shared_secret)
{
POSIX_ENSURE_REF(conn);
if (s2n_tls13_pq_hybrid_supported(conn)) {
POSIX_GUARD(s2n_tls13_compute_pq_hybrid_shared_secret(conn, shared_secret));
} else {
POSIX_GUARD(s2n_tls13_compute_ecc_shared_secret(conn, shared_secret));
}
POSIX_GUARD_RESULT(s2n_connection_wipe_all_keyshares(conn));
/* It would make more sense to wipe the PSK secrets in s2n_tls13_handle_early_secret,
* but at that point we don't know whether or not the server will request a HRR request
* and we'll have to use the secrets again.
*
* Instead, wipe them here when we wipe all the other connection secrets. */
POSIX_GUARD_RESULT(s2n_psk_parameters_wipe_secrets(&conn->psk_params));
return S2N_SUCCESS;
}
int s2n_update_application_traffic_keys(struct s2n_connection *conn, s2n_mode mode, keyupdate_status status)
{
POSIX_ENSURE_REF(conn);
/* get tls13 key context */
s2n_tls13_connection_keys(keys, conn);
struct s2n_session_key *old_key;
struct s2n_blob old_app_secret;
struct s2n_blob app_iv;
if (mode == S2N_CLIENT) {
old_key = &conn->secure.client_key;
POSIX_GUARD(s2n_blob_init(&old_app_secret, conn->secrets.tls13.client_app_secret, keys.size));
POSIX_GUARD(s2n_blob_init(&app_iv, conn->secure.client_implicit_iv, S2N_TLS13_FIXED_IV_LEN));
} else {
old_key = &conn->secure.server_key;
POSIX_GUARD(s2n_blob_init(&old_app_secret, conn->secrets.tls13.server_app_secret, keys.size));
POSIX_GUARD(s2n_blob_init(&app_iv, conn->secure.server_implicit_iv, S2N_TLS13_FIXED_IV_LEN));
}
/* Produce new application secret */
s2n_stack_blob(app_secret_update, keys.size, S2N_TLS13_SECRET_MAX_LEN);
/* Derives next generation of traffic secret */
POSIX_GUARD(s2n_tls13_update_application_traffic_secret(&keys, &old_app_secret, &app_secret_update));
s2n_tls13_key_blob(app_key, conn->secure.cipher_suite->record_alg->cipher->key_material_size);
/* Derives next generation of traffic key */
POSIX_GUARD(s2n_tls13_derive_traffic_keys(&keys, &app_secret_update, &app_key, &app_iv));
if (status == RECEIVING) {
POSIX_GUARD(conn->secure.cipher_suite->record_alg->cipher->set_decryption_key(old_key, &app_key));
} else {
POSIX_GUARD(conn->secure.cipher_suite->record_alg->cipher->set_encryption_key(old_key, &app_key));
}
/* According to https://tools.ietf.org/html/rfc8446#section-5.3:
* Each sequence number is set to zero at the beginning of a connection and
* whenever the key is changed; the first record transmitted under a particular traffic key
* MUST use sequence number 0.
*/
POSIX_GUARD(s2n_zero_sequence_number(conn, mode));
/* Save updated secret */
struct s2n_stuffer old_secret_stuffer = {0};
POSIX_GUARD(s2n_stuffer_init(&old_secret_stuffer, &old_app_secret));
POSIX_GUARD(s2n_stuffer_write_bytes(&old_secret_stuffer, app_secret_update.data, keys.size));
return S2N_SUCCESS;
}
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